The present invention relates to a power tool comprising a clutch movable between an engaged position in which power is transmitted from a drive shaft to an output shaft, and a released position in which there is no power transmission to the output shaft. The invention further relates to a clutch having an actuator for moving the clutch between an engaged position and a released position.
U.S. patent Ser. No. 5,159,522 discloses a clutch cooperating with a drive shaft and having a first disk-shaped clutch element from which the torque of a drive shaft can be transmitted via a friction lining to an associated second clutch element which latter is connected with a drive shaft. The clutch is designed as an electromagnetic clutch wherein a contact pressure is produced by a coil when the latter is suitably driven via a transistor circuit.
A clutch of that kind can be used for numerous operating functions. It is, however, a disadvantage of such a clutch that the power input required for achieving sufficient torque transmission is quite considerable.
There have further been known in the art numerous other clutch types comprising various actuating elements. In the automotive industry, for example, hydraulically operated clutches have been known for many years. Other clutches known include, for example, electric motor-operated clutches and, of course, mechanically operated clutches that are actuated by a lever or the like.
However, power tools, in particular hand held power tools, such as nut runners having a preset shut-off-torque, at which torque transmission is interrupted, need very compact clutches that allow for a high torque transmission, are very reliable, light-weight and have a low power consumption if electrically activated.